[PATCH v2] UBUNTU: SAUCE: Don't register vga16fb framebuffer if other framebuffers are present

Stefan Bader stefan.bader at canonical.com
Fri Mar 26 12:54:07 UTC 2010


Chase Douglas wrote:
> On Fri, Mar 26, 2010 at 4:12 AM, Amit Kucheria
> <amit.kucheria at canonical.com> wrote:
>> On 10 Mar 25, Chase Douglas wrote:
>>> Using the vga16fb framebuffer is not safe when other framebuffers are
>>> present. This fixes the case where the vga16fb module is loaded after
>>> a better framebuffer is loaded (since vga16fb is by definition the
>>> worst-case framebuffer).
>> So what happens in the case where vga16fb is the first one loaded and some
>> other (better) fb is loaded later?
> 
> There's two answers:
> 
> 1. This patch is in vga16fb itself, so it only prevents itself from
> registering as a framebuffer. If vga16fb gets /dev/fb0, any other
> framebuffer can still register further framebuffers.
> 
> 2. That doesn't really matter cause we're screwed if vga16fb is first
> when we try to use KMS. KMS drivers have their own fb, but only
> /dev/fb0 is ever used, so you get bad interactions in that case.
> Thankfully, no one seems to be having this issue anymore because the
> KMS drivers are loaded before vga16fb and module loading is serialized
> by the kernel. If we do find it happens, we may have to tell people to
> blacklist vga16fb manually. All this is secondary to the issue fixed
> by this patch, however.
> 
> -- Chase
> 
I think I will proceed with this by
a) currently test building with it applied
b) test that build on a few local systems
c) if it seems to work include it in this weeks upload but we will need
   to pay close attention on it

-Stefan





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